Sulfonated polyquinoxaline, method for preparing the same, proton exchange membrane and fuel cell

Abstract

The present disclosure relates to a sulfonated polyquinoxaline, which is obtained by polymerization of a dihydrazide monomer with a tetraamine monomer and subsequent by post-sulfonation. The present disclosure also relates to a proton exchange membrane formed from the sulfonated polyquinoxaline and a fuel cell comprising the proton exchange membrane.

Description

Technical Field

[0001] This invention relates to sulfonated polyquinoxaline and its preparation method. The invention also relates to a proton exchange membrane formed from said sulfonated polyquinoxaline and a fuel cell comprising said proton exchange membrane, particularly a direct methanol fuel cell. Background Technology

[0002] Polymer proton exchange membranes (PEMs) play a crucial role in fuel cell systems, separating fuel gases between the two electrodes and transferring protons from the anode to the cathode. Currently, perfluorosulfonic acid PEMs are the only commercially available proton exchange membranes, with the most advanced being the Nafion series from the United States, which possesses excellent proton conductivity, chemical stability, and mechanical properties. However, their high cost and narrow humidity and temperature range limit their widespread application.

[0003] As alternatives to fluorinated polymer electrolyte membranes, non-fluorinated aromatic PEMs have been developed to reduce costs and fuel permeation and improve fuel cell performance at higher temperatures. These include sulfonated polysulfone, sulfonated polyphenylene sulfide, sulfonated polyether ether ketone, sulfonated polybenzimidazole, and sulfonated polyphosphazene. Various non-fluorosulfonic acid polymers offer advantages as alternative membranes, such as relatively low cost, high water absorption over a wide temperature range, and lower environmental pollution from raw materials. However, most of them fail to meet the requirements of high proton conductivity, strong hydrolytic stability, and high dimensional stability at high operating temperatures necessary for high-performance proton exchange membranes. Furthermore, current technologies often employ post-sulfonation methods during the preparation of sulfonated polymers, which frequently suffer from unclear sulfonation sites (making it difficult to precisely control the degree of sulfonation) and overly stringent sulfonation conditions (such as high temperatures leading to excessive polymer degradation).

[0004] To address these issues, existing technologies have attempted to develop novel polymers, such as the sulfonated polyquinoxaline disclosed in CN110669217B, CN110628021B, and CN110655648B. However, further research indicates that when these polymers are used as proton exchange membranes in direct methanol fuel cells, they still suffer from low power density (maximum power density not exceeding 65 mW / cm²). -2 This needs to be improved.

[0005] Therefore, there is still a need to develop new polymers for the preparation of proton exchange membranes to achieve a good trade-off between easily controllable sulfonation degree, high proton conductivity, high hydrolytic stability, high dimensional stability, and high power density. Summary of the Invention

[0006] The present invention was made in view of the above-mentioned problems, and its object is to provide a sulfonated polyquinoxaline with precise sulfonation sites, high hydrolytic stability, high dimensional stability, high proton conductivity and high power density, as well as a proton exchange membrane and fuel cell prepared therefrom, especially a direct methanol fuel cell.

[0007] To address the above problems, a first aspect of the present invention provides sulfonated polyquinoxaline, the chemical structure of which is as follows:

[0008]

[0009] in:

[0010] 0≤x≤1, 0≤y≤1, and x+y=1;

[0011] 5≤n≤300;

[0012] R1 is selected from the following group:

[0013]

[0014]

[0015] Ar1 is selected from the following group:

[0016]

[0017] Ar2 is selected from the following group:

[0018]

[0019] Ar3 is selected from the following group:

[0020]

[0021] In Ar1 and Ar3, X is independently selected from the following groups: O and S;

[0022] Y in Ar2 is selected from the following groups: O, S, SO2, CO.

[0023] A second aspect of the present invention provides a method for preparing sulfonated polyquinoxaline as described in the first aspect, comprising:

[0024] (a) Polymerizing a diacyl monomer with a tetraamine monomer to obtain a non-sulfonated polyquinoxaline; and

[0025] (b) The non-sulfonated polyquinoxaline is sulfonated using a sulfonating agent to obtain the sulfonated polyquinoxaline.

[0026] In one embodiment, the diacyl monomer is selected from the group consisting of:

[0027]

[0028] X is selected from the following group: O, S;

[0029] The Y is selected from the following group: O, S, SO2, CO.

[0030] In one embodiment, the tetraamine monomer is selected from the group consisting of:

[0031]

[0032] In one embodiment, the polymerization in step (a) is carried out in a solvent.

[0033] In one embodiment, the solvent is m-cresol or chloroform.

[0034] In one embodiment, step (a) is performed under inert gas protection.

[0035] In one embodiment, the sulfonating agent in step (b) is fuming sulfuric acid or concentrated sulfuric acid.

[0036] A third aspect of the present invention provides a diacyl monomer with the following chemical structure:

[0037]

[0038] A fourth aspect of the invention provides a proton exchange membrane formed of sulfonated polyquinoxaline according to the first aspect.

[0039] The fifth aspect of the invention provides a fuel cell, particularly a direct methanol fuel cell, comprising a proton exchange membrane according to the fourth aspect.

[0040] The beneficial technical effects of this invention are as follows:

[0041] The reaction conditions are simple and mild, with controllable sulfonation. The resulting polymers typically exhibit good solubility in DMAC and DMSO, and demonstrate excellent thermal hydrolytic stability and good dimensional stability over a wide temperature range. More importantly, the polymers synthesized in this invention can achieve 80 mW / cm² performance when used in direct methanol fuel cells. -2 The above maximum power density is precisely the property required by PEM.

[0042] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0043] Figure 1 These are the infrared spectra of sulfonated polyquinoxaline from Examples 1-5.

[0044] Figure 2 These are the NMR spectra of sulfonated polyquinoxaline from Examples 1 and 3.

[0045] Figure 3 This is the NMR spectrum of the diacyl monomer 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl (POBZOTP).

[0046] Figure 4 This is the infrared spectrum of the diacyl monomer 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl (POBZOTP).

[0047] Figure 5 This is a performance comparison chart of a direct methanol fuel cell using sulfonated polyquinoxaline (Example 3) as the proton exchange membrane and a direct methanol fuel cell using a polymer from the prior art as the proton exchange membrane. Detailed Implementation

[0048] Embodiments of this disclosure will now be described in more detail. While certain embodiments are provided in this disclosure, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0049] In this disclosure, "range" is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] The terms "first," "second," etc., used in this disclosure are used merely for clarity of description to distinguish between objects and do not limit the size, quantity, or other order of the objects they describe. Directional terms indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are used solely for the purpose of describing this disclosure, not to indicate or imply that the objects referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this disclosure.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0052] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0053] Unless otherwise specified, the terms “comprising,” “including,” “having,” “containing,” or any other variations thereof used in this disclosure are intended to cover non-exclusive inclusion.

[0054] Unless otherwise specified, the indefinite articles “a” and “an” preceding an element or component in this disclosure do not impose any limitation on the quantity requirement (i.e., the number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity is clearly intended to define the singular form.

[0055] As mentioned above, existing proton exchange membranes still face the challenge of achieving a good trade-off between controlling the degree of sulfonation, high proton conductivity, high hydrolytic stability, and high dimensional stability, which urgently needs to be addressed.

[0056] Sulfonated polyquinoxaline

[0057] To at least partially address one or more of the aforementioned problems and other potential issues, a first exemplary embodiment of this disclosure provides sulfonated polyquinoxaline with the following chemical structure:

[0058]

[0059] in:

[0060] 0≤x≤1, 0≤y≤1, and x+y=1;

[0061] 5≤n≤300;

[0062] R1 is selected from the following group:

[0063]

[0064] Ar1 is selected from the following group:

[0065]

[0066] Ar2 is selected from the following group:

[0067]

[0068] Ar3 is selected from the following group:

[0069]

[0070] In Ar1 and Ar3, X is independently selected from the following groups: O and S;

[0071] Y in Ar2 is selected from the following groups: O, S, SO2, CO.

[0072] Method for preparing sulfonated polyquinoxaline

[0073] To at least partially address one or more of the aforementioned problems and other potential problems, a second exemplary embodiment of this disclosure provides a method for preparing sulfonated polyquinoxaline, comprising:

[0074] (a) Polymerizing a diacyl monomer with a tetraamine monomer to obtain a non-sulfonated polyquinoxaline; and

[0075] (b) The non-sulfonated polyquinoxaline is sulfonated using a sulfonating agent to obtain the sulfonated polyquinoxaline.

[0076] Regarding the diacyl monomer, it can be selected from the following group:

[0077]

[0078]

[0079] X is selected from the following group: O, S;

[0080] The Y is selected from the following group: O, S, SO2, CO.

[0081] The tetraamine monomer can be selected from the following group:

[0082]

[0083] The polymerization in step (a) can be carried out in a solvent, preferably m-cresol or chloroform.

[0084] Step (a) can be performed under the protection of an inert gas.

[0085] The sulfonating agent in step (b) can be fuming sulfuric acid or concentrated sulfuric acid.

[0086] Monomers used to prepare sulfonated polyquinoxaline

[0087] To at least partially address one or more of the aforementioned problems and other potential issues, a third exemplary embodiment of this disclosure provides a diacyl monomer with the following chemical structure:

[0088]

[0089] Proton exchange membrane

[0090] In order to at least partially address one or more of the above-mentioned problems and other potential problems, a fourth exemplary embodiment of this disclosure provides a proton exchange membrane formed of sulfonated polyquinoxaline according to a first exemplary embodiment of this disclosure.

[0091] fuel cells

[0092] In order to at least partially address one or more of the above-mentioned problems and other potential problems, a fifth exemplary embodiment of this disclosure provides a fuel cell, particularly a direct methanol fuel cell, which includes a proton exchange membrane as described in a fourth exemplary embodiment of this disclosure.

[0093] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0094] Example 1

[0095] The diazoyl monomer 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl (POBZOTP) was prepared by the following specific method.

[0096] (1) Preparation of [1,1':4',1”-terphenyl]-4,4”-diol

[0097] 4.72 g (20 mmol) of 1,4-dibromobenzene, 8.28 g (60 mmol) of (4-hydroxyphenyl)boric acid, 11 g (80 mmol) of potassium carbonate, and 0.46 g (0.4 mmol) of tetrakis(triphenylphosphine)palladium were added to a 500 mL flask. Nitrogen gas was introduced, and 300 mL of dioxane was added. The reaction mixture was heated to 85 °C under a nitrogen atmosphere and reacted for 72 h. After cooling to room temperature, the organic solvent was evaporated. The mixture was poured into water at pH 1, filtered, and placed in ethanol and heated to 65 °C under reflux. After cooling to room temperature, it was filtered and dried to give 3.99 g of the white product [1,1':4',1”-terphenyl]-4,4”-diol.

[0098] (2) Preparation of 1-(4-fluorophenyl)-2-(4-phenoxyphenyl)ethane-1,2-dione

[0099] 8.400 g (approximately 0.063 mol) of anhydrous AlCl3 and 54 mL (approximately 0.060 mol) of phenyl ether were added to a 100 mL three-necked flask purged with N2. The mixture was stirred for 20 min in an ice-water bath, and then 10.255 g (approximately 0.060 mol) of 4-fluorophenylacetyl chloride was added dropwise at a rate of one drop per second. After the addition was complete, the reaction mixture was stirred at room temperature for 5 h, and then the reaction solution was slowly poured into 10% dilute hydrochloric acid. The mixture was filtered, washed with water until neutral, and dried to obtain 8.57 g of a white solid, which was 2-(4-fluorophenyl)-1-(4-phenoxyphenyl)ethyl ketone.

[0100] 8.57 g (approximately 0.04 mol) of 2-(4-fluorophenyl)-1-(4-phenoxyphenyl)ethyl ketone and 50 ml of DMSO were added to a 100 ml flask. After all the solid was dissolved, 18.315 g (approximately 0.082 mol) of CuBr2 was added. The reaction system was then heated to 80 °C and reacted for 24 h. The reaction solution was then slowly added to 10% dilute hydrochloric acid, precipitating a yellow solid. After washing until neutral, the solid was filtered and dried to obtain 8.5 g of 1-(4-fluorophenyl)-2-(4-phenoxyphenyl)ethane-1,2-dione.

[0101] (3) Preparation of the diazoyl monomer 4,4'-bis(4-2-4-(4-phenoxy(thiol)phenyl)phenyl)azoyl)phenoxy(thiol)terphenyl

[0102] 7.988 g (approximately 0.035 mol) of 1-(4-fluorophenyl)-2-(4-phenoxyphenyl)ethane-1,2-dione, 3.166 g (approximately 0.017 mol) of [1,1':4',1”-terphenyl]-4,4”-diol, 4.976 g (approximately 0.036 mol) of anhydrous K2CO3 and 20 mL of DMAc were sequentially added to a 100 mL three-necked flask purged with N2. The reaction system was then heated to 130 °C and reacted for 24 h. The reaction solution was then slowly poured into deionized water to obtain a white solid. The solid was recrystallized from acetone and dried to obtain 11 g of monomer 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl (POBZOTP).

[0103] The specific preparation method for proton exchange membranes is as follows:

[0104] (1) Aggregation

[0105] Weigh out 0.92 g of 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl and 0.2303 g of 3,3',4,4'-tetraaminobiphenyl, mix them, pour the mixture into a flask, add 11.2 ml of m-cresol to dissolve it, and react at 120 °C for 24 h under a nitrogen atmosphere. Then pour the solution into methanol to precipitate the polymer. Wash repeatedly until clean, filter, collect the solid, and dry under vacuum to obtain polymer fibers.

[0106] (2) Sulfonation

[0107] The polymer fibers were poured into a flask, and concentrated sulfuric acid was added at a solid content of 10 wt%. The reaction was carried out at 50°C under a nitrogen atmosphere for 5 hours. The reaction solution was then poured into water, and the sulfonation product precipitated. The product was washed repeatedly until the pH reached 5-6. An appropriate amount of sodium carbonate was added, and the product was washed until neutral. The solid was collected by filtration and dried under vacuum to obtain the sulfonated polymer in the form of a sodium metal salt.

[0108] (3) Preparation of proton exchange membranes;

[0109] The sulfonated polymer was dissolved in DMSO at a ratio of 7 wt%, filtered, and degassed. The filtrate was slowly poured onto an ultra-flat glass dish and kept at a low temperature for 4 hours, followed by a high temperature for 12 hours. After the incubation period, deionized water was added to the glass dish to remove the membrane. The membrane was then removed and immersed in 1 mol / L water. -1 In sulfuric acid solution, reacts with H + After sufficient replacement, the membrane is removed and washed with deionized water to remove sulfuric acid, then dried to obtain a proton exchange membrane.

[0110] The chemical structure of the obtained proton exchange membrane is as follows:

[0111]

[0112] Where n = 72.

[0113] Example 2:

[0114] The preparation method for the proton exchange membrane was basically the same as in Example 1, except that the polymerization raw materials were different. Specifically, 0.92 g of 4,4'-bis(4-(2-(phenyl)azoyl)phenoxy)terphenyl and 0.2812 g of 3,3',4,4'-tetraaminobiphenyl were weighed, mixed, and poured into a flask for polymerization. All other steps were the same as in Example 1.

[0115] The chemical structure of the obtained proton exchange membrane is as follows:

[0116]

[0117] Where n = 98.

[0118] Example 3:

[0119] The preparation method for the proton exchange membrane was basically the same as in Example 1, except that the polymerization raw materials were different. Specifically, during polymerization, 1.2596 g of 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl (POBZOTP) and 0.1683 g of 4,4'-bis(2-phenylethylenedione)diphenyl ether were weighed in a 2:1 molar ratio, then mixed with 0.4611 g of 3,3',4,4'-tetraaminobiphenyl and 28 ml of m-cresol, and poured into a flask for polymerization. All other steps were the same as in Example 1.

[0120] The chemical structure of the obtained proton exchange membrane is as follows (where x:y = 2:1):

[0121]

[0122] Where n = 91.

[0123] Example 4:

[0124] The polymer synthesized in this embodiment has a similar structure to that in Example 3, the difference being the degree of sulfonation. The structure is as follows (where x:y = 2:1):

[0125]

[0126] Where n = 88.

[0127] The specific preparation method is as follows:

[0128] (1) Aggregation

[0129] During polymerization, 1.2596 g of 4,4'-bis(4-(2-(4-phenoxyphenyl)azoyl)phenoxy)terphenyl and 0.1683 g of 4,4'-bis(2-phenylethylenedione)diphenyl ether were weighed out in a 2:1 molar ratio. These were then mixed with 0.4611 g of 3,3',4,4'-tetraaminobiphenyl and 28 ml of m-cresol, and poured into a flask. The reaction was carried out at 120°C for approximately 24 hours under a nitrogen atmosphere. The solution was then poured into methanol to precipitate the polymer. The polymer was repeatedly washed until clean, filtered, and the solid was collected and dried under vacuum to obtain polymer fibers.

[0130] (2) Sulfonation

[0131] The polymer fibers were poured into a flask, and fuming sulfuric acid was added at a solid content of 10-15 wt%. The reaction was carried out under a nitrogen atmosphere. The reaction solution was poured into water, and the sulfonation product precipitated. The product was washed repeatedly until the pH was 5-6. An appropriate amount of sodium carbonate was added, and the washing continued until neutral. The solid was collected by filtration and vacuum dried to obtain the sulfonated polymer in the form of a metal salt.

[0132] (3) Preparation of proton exchange membranes;

[0133] The sulfonated polymer was dissolved in DMSO at a ratio of 5 wt%, filtered, and degassed. The filtrate was slowly poured onto an ultra-flat glass dish and kept at 80°C for 4 hours, followed by 120°C for 12 hours. After the incubation period, deionized water was added to the dish to remove the membrane. The membrane was then immersed in 1 mol / L water. -1 In sulfuric acid aqueous solution, with H + After sufficient replacement, the membrane is removed and washed with deionized water to remove sulfuric acid, then dried to obtain a proton exchange membrane.

[0134] Example 5:

[0135] The polymer synthesized in this embodiment has a similar structure to that in Example 4, except that the polymerization raw materials are different. The structure is as follows (where x:y = 2:1):

[0136]

[0137] Where n = 76.

[0138] Specific preparation method:

[0139] During polymerization, 1.2590 g of 4,4'-bis(4-2-4-(4-phenoxyphenyl)phenyl)azoyl)phenoxy)terphenyl and 1.1075 g of 2,2'-((sulfonylbis(4,1-phenylenesulfonyl))bis(4,1-phenylene))bis(1-phenylethane-1,2-dione) were weighed out in a 2:1 molar ratio. These were then mixed with 0.4290 g of 3,3',4,4'-tetraaminobiphenyl and 39 ml of m-cresol, and poured into a flask for polymerization. The remaining sulfonation and film-forming steps were the same as in Example 1.

[0140] The performance of the proton exchange membranes prepared in Examples 1-5 above was tested, as follows:

[0141] Test methods

[0142] 1. The degree of polymerization n mentioned above was determined by measuring the intrinsic viscosity of the polymer using the viscometry method. The specific testing procedure is as follows: Approximately 150 mg of dried polymer was weighed, and a series of polymer solutions were prepared using dimethyl sulfoxide. The outflow time of the solutions and pure solvents was measured using an Ubbelohde viscometer. The relative viscosity η was calculated using Equation 1.1. r .

[0143]

[0144] In the formula η r The relative viscosity of the polymer (dL g) -1 ); t0 and t are the flow times (s) of the blank sample DMSO and the polymer, respectively, and c = 0.5.

[0145] Calculate the specific viscosity (η) sp =η r -1), specific viscosity (η) sp / c) and specific logarithmic viscosity (lnη) r / C). Under conditions of infinite dilution, the limiting values ​​of specific viscosity and specific logarithmic viscosity are called intrinsic viscosity ([η]), and their relationship with concentration can be described by the following empirical formula:

[0146] Huggins equation:

[0147] Kraemer equations:

[0148] Plotting values ​​against concentrations and extrapolating to the intercept at zero concentration yields the intrinsic viscosity ([η]). The polymer molecular weight M is calculated using the Mark-Houwink equation.

[0149] [η]=KM a

[0150] Where K = 10-4 a = 0.7.

[0151] The degree of polymerization, n, is the ratio of the polymer's molecular weight to the molecular weight of the repeating unit.

[0152] 2. The IEC is obtained by acid-base titration. The specific determination process is as follows: Weigh 100-200 mg of proton exchange membrane, vacuum dry for 8 hours, and record the weight as m. Then, immerse the sample in 50 mL of 15 wt.% NaCl aqueous solution for 72 hours, and then use 0.02 mol L... -1 Titration with standard sodium hydroxide solution was performed using phenolphthalein as an indicator, and the volume of standard sodium hydroxide solution consumed was recorded. The calculation formula is shown in Figure 1.2:

[0153]

[0154] Where: IEC represents ion exchange capacity (meq g) -1 );V NaOH The titration volume (mL) of the sodium hydroxide solution; C NaOH The molar concentration of the sodium hydroxide solution (0.02 mol L) -1 m: mass of dry film (g).

[0155] 3. The water absorption rate is obtained based on the mass change of the proton exchange membrane when it is immersed in water.

[0156] The specific process is as follows: Weigh 150 mg of the membrane sample, dry it under vacuum at 120℃ for 8 hours, and then weigh it quickly. The mass is recorded as W. d The membranes were immersed in deionized water at 30℃ for 12 hours. After the samples were fully immersed, the surface moisture was quickly wiped off with absorbent paper, and the membranes were weighed immediately using an analytical balance. The mass was recorded as Ws. After weighing, the membranes were immersed in deionized water again for at least 20 minutes. This process was repeated three times, and the average value was taken. The water absorption rate was calculated using Equation 1.3.

[0157]

[0158] W d and W s The values ​​represent the membrane mass under dry and fully hydrated conditions, respectively.

[0159] 4. The dimensional change rate is obtained based on the changes in length, width, and thickness of the proton exchange membrane when immersed in water. It is mainly used to determine the dimensional stability of the membrane, referring to the rate of change in the thickness and length of the wet membrane compared to its initial state when the proton exchange membrane reaches saturation after absorbing water. The measurement process is as follows: A membrane of uniform thickness is cut into 2×3cm pieces. 2 The thickness and length of the rectangular strip were measured by taking multiple measurements and averaging them, and recorded as t. d and ld The membrane was soaked in an aqueous solution at 30℃ for 12 hours. After soaking, it was quickly removed, its surface moisture was wiped dry, and the thickness and length of the membrane were measured and recorded as t and l, respectively. The dimensional change rates of the membrane thickness and membrane plane were calculated using equations 1.4 and 1.5, respectively.

[0160]

[0161] In the formula Δt c : Dimensional change rate in the thickness direction of the film; Δl c : Dimensional change rate along the membrane length direction; l d and t d : Initial length and thickness (mm) of the dry film sample; l and t: Thickness and length (mm) of the sample after water absorption.

[0162] 5. The proton conductivity σ was determined by measuring the impedance coefficient of the proton exchange membrane using an electrochemical impedance spectroscopy (EIS) and calculated according to Formula 1.5. A four-electrode Hiokki 3536 EIS was used, with a frequency range of 10-100 kHz. The specific testing procedure was as follows: A uniform proton exchange membrane was selected and cut into rectangular strips of 1.5 × 0.5 cm. These strips were sandwiched between platinum electrode plates spaced 0.5 cm apart and fixed onto a polytetrafluoroethylene (PTFE) plate. The assembled device was immersed in deionized water at different temperatures for 15 minutes. The wires connecting the platinum electrodes at both ends were then connected to the EIS. The frequency was set to 10-100 kHz, and the impedance coefficient R of the membrane at different temperatures was measured. The result was then calculated using Formula 1.6.

[0163]

[0164] In the formula, σ represents the proton conductivity of the proton exchange membrane (mS / cm). -1 ); d: distance between the two electrodes 0.5cm; t s and w s R represents the membrane thickness and width measured at 20°C and 20% RH; R is the measured impedance value.

[0165] 6. Performance test of direct methanol fuel cell power generation. Test conditions: 80℃, feed of O2 and 10wt% methanol.

[0166] Test Results

[0167] The test results for water absorption rate, dimensional change rate, and proton conductivity are shown in Table 1 below.

[0168] Table 1

[0169]

[0170] aThe values ​​in parentheses are calculated values, while the values ​​in parentheses are measured values. b Water absorption rate measured at 30℃ c Dimensional transformation rate measured at 30℃ d Measured in water.

[0171] As can be clearly seen from Table 1, the theoretical IEC of the proton exchange membrane of the present invention is almost identical to that of the measured IEC, achieving precise control over the degree of sulfonation. In addition, the water absorption rate, dimensional change rate and conductivity of these membranes are all within the ideal range, thus achieving significant and beneficial technical effects.

[0172] The test results of the power generation performance of direct methanol fuel cells are as follows: Figure 5 As shown in Table 2 below.

[0173] Table 2. Maximum power density, open-circuit voltage, and output voltage of direct methanol fuel cells using different polymers.

[0174]

[0175] Note: Example 3 is the polymer of Example 3 in this invention; Comparative Sample 1 is the polymer of Example 4 in patent CN110669217B; Comparative Sample 2 is the polymer of Example 3 in patent CN110628021B; Comparative Sample 3 is the polymer of Example 2 in patent CN110655648B.

[0176] As can be clearly seen from Table 2, the maximum power density of the fuel cell using the proton exchange membrane of the present invention can reach 80 mW / cm². -2 The above is far superior to existing technologies, thus achieving significantly beneficial technical effects.

[0177] The foregoing examples are merely illustrative, intended to explain certain features of this disclosure. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are merely illustrative of selected implementations based on combinations of all possible embodiments. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of this application. As used in the claims, the term "comprising" and its semantic variations logically also include different and varying terms, such as, but not limited to, "basically constitutes" or "consisting of." Numerical ranges are provided where necessary, and these ranges also include subranges within them. Variations within these ranges are also self-evident to those skilled in the art and should not be considered as a donation to the public, and such variations should be interpreted as being covered by the appended claims where possible. Furthermore, advancements in technology may result in alternatives or sub-equivalents not currently considered due to inaccuracies in linguistic expression, and such variations should also be interpreted as being covered by the appended claims where possible.

Claims

1. Sulfonated polyquinoxaline, with its chemical structure as follows: Where: 0 < x ≤ 1, 0 ≤ y < 1, and x + y = 1; 5≤n≤300； R1 is selected from the following group: ； ； ； ； ； ； ； Ar1 is selected from the following group: ； ； Ar2 is selected from the following group: ； ； ； ； Ar3 is selected from the following group: ； ； ； ； X in Ar1 and Ar3 are each independently selected from the following group: O, S; Y in Ar2 is selected from the following group: O, S, SO2, CO.

2. A method for preparing the sulfonated polyquinoxaline according to claim 1, which comprises the following steps: (a) Reacting a diacyl monomer with a tetraamine monomer to obtain a non-sulfonated polyquinoxaline; and (b) Sulfonating the non-sulfonated polyquinoxaline using a sulfonating reagent to obtain the sulfonated polyquinoxaline.

3. The method according to claim 2, wherein the diacyl monomer is selected from the following group: 、 、 、 、 、 、 、 、 、 、 、 ； The X is selected from the following group: O, S; The Y is selected from the following group: O, S, SO2, CO.

4. The method according to claim 2, wherein the tetraamine monomer is selected from the following group: 、 、 、 。 5. The method according to claim 2, wherein the polymerization in step (a) is carried out in a solvent, and the solvent is m-cresol or chloroform.

6. The method according to claim 2, wherein step (a) is carried out under the protection of an inert gas.

7. The method according to claim 2, wherein the sulfonating reagent in step (b) is fuming sulfuric acid or concentrated sulfuric acid. ​ ​ ​

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